1. Field of the Invention
The present invention relates generally to ESD protection devices for the magnetoresistive (MR) read head sensor of a magnetic head, and more particularly to the use of silicon germanium (SiGe) and silicon germanium carbon (SiGeC) transistors as ESD protection devices that are placed across the electrical leads of a GMR sensor.
2. Description of the Prior Art
Magnetoresistive (MR) sensors are commonly used as read elements in thin film magnetic heads for sensing recorded signals on a magnetic medium, such as a magnetic disk. A thin film magnetic head which incorporates an MR sensor is called an MR head, and such MR heads are fabricated on devices termed sliders that are disposed within hard disk drives in close proximity to magnetic disks within the drive. When a magnetic medium, such as a magnetic disk is rotated adjacent the MR sensor, magnetic fields from the disk induce a response in the MR sensor causing the sensor to change its resistance. A sense current conducted through the MR sensor changes its magnitude proportionally to the change in resistance, and the magnitude changes are then processed by channel electronics into playback signals representing information stored on the magnetic medium.
A typical MR sensor is generally approximately 5 microns long, 1 micron high and 200 Angstroms thick. The length and thickness of the MR stripe are exposed at a surface of an MR head while the height is buried in the head body. During construction and assembly of the MR head, the MR sensor must be protected from electrostatic discharge (ESD), as a discharge of only a few volts can destroy or severely damage the MR sensor. Such a discharge can occur by contact with or close proximity to a person, during steps involved in the fabrication, or from components of a disk drive. The prior art teaches the use of electrical elements to protect MR sensors from ESD. These elements include diodes which shunt excessive current away from the MR sensor to larger conductive components in the head via leads which are connected to the MR sensor. Such larger components may include shield or coil layers that form part of an integrated MR head.
A prior art improvement in ESD protection of MR sensor includes the fabrication of magnetic heads on sliders using thin film technology, combined with the construction of ESD protection elements on a silicon wafer by integrated circuit technology. Such prior art ESD protection devices are described in U.S. Pat. No. 5,587,857, the disclosure of which is incorporated herein as though set forth in full. Significantly, as disk drive technology has advanced, magnetic head components have decreased in size in order to increase the data areal storage density of the disk drive, and as a result, advanced MR sensors, termed giant magnetoresistive (GMR) sensors, have been developed. Such GMR sensors have smaller components and lower ESD thresholds than prior art MR sensors, such that an ESD event of less than even one volt can cause permanent damage to the GMR sensor component. The prior art ESD protection devices, such as silicon diodes described in the above-mentioned ""857 patent, have ESD protection thresholds of approximately 1.4 volts, such that these prior art ESD protection devices are not capable of fully preventing ESD damage to the advanced GMR sensor components. A need therefore exists for the development and implementation of ESD protection devices having lower ESD voltage thresholds in order to protect sensitive GMR sensor components. The present invention utilizes silicon germanium (SiGe) and silicon germanium carbon (SiGeC) integrated circuit devices for ESD protection, in that such devices have sufficiently low threshold voltages to provide needed ESD protection for GMR sensors.
The present invention includes a GMR head on a slider which is protected from ESD damage by SiGe and/or SiGeC integrated circuit elements, preferably by Heterojunction Bipolar Transistors (SiGe HBT and/or SiGeC HBT) that are generally referred to herein as silicon germanium circuit devices. In a preferred embodiment a silicon chip, containing the SiGe circuit device is located on the trailing edge of the slider. A thin film GMR head is located on the trailing edge of the silicon chip so that when the GMR head is constructed, interconnects can easily be made with the integrated circuit elements. In an alternative embodiment the GMR head is constructed on the trailing edge of the slider and the silicon chip with its ESD protection device is mounted adjacent the GMR head making electrical connections through pre-formed pads. The SiGe circuit device may be electrically connected in different configurations, including a diodic configuration, an npn mode, a series cascade configuration and a two stage ESD network configuration.
A series of steps are provided for mass producing the GMR head on a slider with ESD protection. Integrated circuit technology is employed to construct the SiGe circuit device for multiple GMR heads on a silicon wafer. In a preferred embodiment this silicon wafer is fixedly attached to a wafer of slider material to provide a composite wafer. Using thin film technology a series of GMR heads are constructed on top of the silicon wafer with electrical connections being made to the SiGe circuit devices. The composite wafer is then diced into quadrants, each quadrant containing rows and columns of sliders. Each quadrant is then diced into rows, each row containing a row of sliders. Each row is then lapped which forms an air bearing surface (ABS) for each slider. Each row is then diced into individual sliders which is the completed product.
An object of the present invention is to provide an MR head which is connected to an SiGe integrated circuit device on a slider.
Another object is to provide a GMR head which is protected from ESD by SiGe HBT and/or SiGeC HBT devices on a slider.
A further object of the present invention is to provide a GMR head which is protected from ESD by SiGe HBT and/or SiGeC HBT transistor devices that are placed across the electrical leads of the GMR head.
Yet another object is to provide a method of merging thin film and integrated circuit technologies for mass producing GMR heads on sliders which are protected from ESD by SiGe HBT and/or SiGeC HBT integrated circuit devices.
Other objects, advantages and features of the invention will be readily apparent after reviewing the following specification, claims and accompanying drawings.